MTH NYC Hudson smoke pcb repair

Jim, if you have any soldering skills at all it should be an easy fix. You will want to scrape away the green coating on either side of the break. Then tin the exposed copper and bridge the gap with a piece of wire and solder it to the board. No need for a new unit.

Pete

You can also just follow the traces to the soldered connection and use a jumper wire between the previous connection points.

Welcome Jim...you will get your answers here and fast response is the "norm" here.

I'd be interested in seeing a photo of the "circuit break".

Thank you for the quick replies to my small problem. I'm one of those 'I'd rather fix it myself' guys and they say great minds think alike. My thoughts after joining this forum, were to try and take a piece of bell wire and make the repair. That was after I found out that a new unit could not be purchased right now. I even called Nicholas Smith trains and asked about buying parts from them for MTH. The gal said they don't do the repairs there, but a guy comes in once a week and picks up whatever people leave with them for repairs. I checked the resistors and the still measured about 19-20 ohms. They are brittle and crusty, but I'll try to clean them up for resoldering. I remember reading a comment about someone on this forum about making a similar repair to a pc board, but I couldn't find it again. So I figured I should join the group and get involved with my trains again. I'll try to add a couple of pictures of what I am working with. I'll post again later after my attempt to repair (I've never tried to repair a pc board before).

Jim.

Sorry for the picture duplication. Don't know how I did that yet.

Jim.

A different subject, but one you touched upon.  You said "Protosounds," which usually means PS1, from roughly before 2000.  How old are the batteries?  If they're over 5-6 years old, dispose of them promptly.  PS1 can develop problems from bad batteries.

That's a bit more than a "circuit break"!  It looks like something went nuts and overheated the resistors.  I suspect that maybe a component has failed on the board and is putting full voltage across the resistors, that circuit is supposed to regulate the power to the resistors.

The missing copper is supposed to support the resistors as well as provide conductivity.  You can probably cobble something up, but that's quite a bit of PCB damage.

I just finished trying to solder fine strands of copper wire to the resistors and to the broken foils. When activated, it threw the circuit breaker on the transformer. The FET was extremely hot. No smoke or sparks though. I looked very closely at the circuits and could see that a fine soldered line going down the left edge of the top of the board. It looked like it might have been connected to the 'left' side of the resistors. Left meaning to the left of the smokestack. So I connected that thin soldered line to the left side foil. After the breaker tripped, I said maybe it doesn't go there. Although that part of the circuit on top of the board is gone. I looked a little closer and saw that the input voltage was AC, not DC like I thought. I measured about 5 volts going into the board. That input is directly connected to an integrated circuit marked DF04 with markings showing ~ current on one side and + and - on the output side. I had tried to short out the + and - by soldering a wire from the fine soldered line that is connected to the minus output side of the IC to the + side of the resistors. I cut the wire I had connected and the board seems to work correctly-almost. The 'negative ' soldered line that I had incorrectly attached to the positive side of the resistors is now not connected and the fan motor doesn't operate now. The fan did operate before I tried to fix. Sounds familiar huh? It seems like the resistors are heating up now, although not cherry red hot. I'm wondering where I should try and connect the fine soldered line to get the fan working again. I would include another picture of my repairs, but it looks so bad as to be embarassing.

Jim. 

Just to check myself, I just hooked the pc board back up to recheck what I said the voltages were. I did measure about 5 volts going into the board. The resistors are not heating up. The fan doesn't run. I might be able to figure it out if I could see a non- damaged board to see how the circuits should go. Does anybody know what voltage the resistors are supposed to receive?

New message! I figured that this board might be toast, so I went back and soldered a jumper from the fine soldered line on the left side of the board to the output side of the resistors on the right side. No sparks or thrown breakers. That was good. The resistors glowed a low cherry red. I plugged the fan connector back on and it worked! Next will be to put it back together without the body and run it with fluid in it. I'm pretty sure I didn't run it with enough smoke fluid and it probably over heated. I'll report back.

Jim.

Note the resistors are NOT connected together on the right side of the photo.  If by FET you are referring to Q2 on the component side, that's just a transistor which you are replace if need be.  The purpose Q2 is to disable/enable one of the heater resistors depending on the track voltage.  This effects a simple regulator.

That board is a common board and should still be available.  I would replace those smoke elements they are readily available also.

The board doesn't regulate voltage, rather it shorts one of the series resistors out when voltage is below 13V.  Above 13V the resistor is kicked in an overall resistance is 32 ohms, vice just 16 under 13V.

Look at the larger 3 legged transistor and see if it is shorted.  Could be, or the unit was run dry and burned up.

You can still follow traces and use jumper wires.

Make sure the rectifier is making DC voltage, check the fan output for 5VDC.   G

Well, as a follow up. It worked okay. I put smoke fluid in it and saturated the wick and ran it for several minutes. It is working just like new. I put everything back together and put it away for now. Both of my MTH trains have replacement battteries that are about 5-6 years old. They both took a charge and are operating properly for now. I wonder if the twin resistors can be changed to a single resistor like Lionel uses. We'll see. This is a neat forum and I will try to be a good member. Thanks for your help.

Jim. 

Stan, thanks for the photo of the board. I'm not sure I understand how the shorting of one resistor works, it sounds reasonable. I ran a jumper over to the output side of the resistors that are now wired in parallel. Everything works, but for how long? Could be a potential fire hazard that I will monitor closely under operation. Besides, I don't like to run the smoke all the time I run it because of smoke saturation in the porch where I am only allowed to run the trains-on the floor like a little kid. I'm getting too old to be on my kness for long periods of time now. LOL. Where can these parts be purchased now? Are they train show items? I'd like to get new heater elements too.

GGG, I looked closely at the FET and it looked okay, but got quite hot while I had the board wired wrong. I guess lucky for me, the breaker tripped on the transformer. Now that all functions are working (except for the one resistor being wired wrong), I guess I'll wait until it fails again. Meanwhile, I'll keep my eyes open for the replacement parts. Thanks again.

Jim.

Since the primitive regulation scheme involves switching in the second series resistor for higher voltages, the answer is no, you'd likely end up with more charring of the board.

Houston, we have a problem.

Some background.  The higher the voltage the higher the power/heat.  The lower the net heater resistance, the more power/heat is generated.  In other words there are two things going on in that affect heat, (1) track voltage and (2) the net heater resistance.

As GGG notes, the Q2 transistor switches in the 2nd resistor when the track voltage reaches a threshold.   So to use your measurement of 20 ohm resistors, at low track voltage the net heater is 20 ohms (only one resistor active); at high track voltage the heater is 20+20=40 ohms (both resistors active but in series).  So the effect of the increased voltage is crudely demoted by the additional net resistance.  That's about as a "simple" a regulator as you can make.

If you are seeing BOTH resistor "cherry-red" at low track voltage and/or you wired the two resistors in parallel, then those resistors are not long for the world.  In other words you have an effective heater resistance of 20/2=10 ohms which does not change even when track voltage exceeds the simple regulator trip voltage.  So as soon as you run the engine at running speeds with smoke on, those resistors will likely overheat and fail or the circuit board will further burn up.

Those resistors are normally 16 ohms in PS/1 smoke units.

PS-2 also.  G

Isn't it really current regulation.  Voltage is constant output from the bridge based on input voltage.  But current is cut in half when the second resistor cuts in.  G

Correct, and if we're being picky, PS/3 as well.   Since we're talking about a PS/1 unit, that's what I was addressing.